When I need to write something, and I have a computer, and something is inconvenient, I can quickly (well, within minutes, maybe 30 of them) alter it to my liking, and return to writing.

When I only have a pen and paper (which I used extensively for writing at school), many things may be inconvenient, but there's no way to fix it. This may turn into a source of a low-key stress, and interfere with my writing much more than tweaking a computer would.

I use Emacs, an ultimate tweaker's tool, for writing every day. Last time I had to tweak something in it was a few weeks ago, and it took maybe 2-3 minutes. It's a small price to pay for a tool that just does what you need, when you need it, with zero mental load, and zero frustration.